Acoustic signal transducers



March 8, 1960 w. F. KNAUERT 2,927,977

ACOUSTIC SIGNAL TRANSDUCERS Filed Nov. 17, 1958 2 Sheets-Sheet 1 ITM/@NIW March 8, 1960 w. F. KNAUERT 2,927,977

ACOUSTIC SIGNAL TRANSDUCERS Filed Nov. 1'7, 1958 2 Sheets-Sheet 2 n 55 I Armen/9.11

UnitedStates Patent Q Acousrrc SIGNAL rinnvsnucrzns y William F. Knanert, Yonkers, N.Y., assignor to Sonotone gorporation, Elmsford, N.Y., a corporation of New Application November 17, 1958, Serial No.V 774,437 v Claims. (Cl. 179-115) This invention relates to acoustic signal transducers of Fig. 4 is a simplified diagrammatic view showing the relationship of the ferromagnetic elements and the windthe type described in U.S. Patent 2,432,424, which transduce acoustic signals into electric signals or electric signals 1nto acoustic signals.

volume dimensions ofwhich should not exceed about -i/l X x 1/2, so as to make it possible to combine two such transducers, `one operating as a microphone and the other as a receiver, togetherwith all operating components of a multi-stage transistor-amplifier, into a minute volume itting into a temple of an eyeglass frame or into a tiny casing fitting behind the outer ear or within the cavity of the outer ear of the user.

ln such acoustic signal transducers, arl-acoustic diaphragm is connected to drive or be driven by a at ferro magnetic armature or reed which is surrounded by a spool with transducing windings and is arranged to vib rate between one or two pairs of closely-spaced opposite poles of a ferromagnetic core for operation either as a microphone or receiver in transducing vibrations of an acoustically excited diaphragm into corresponding electric signals and vice versa. For efficient operation of 'such miniature transducers, the tiny flat reed must vibrate Within a tiny, iiat central spool compartment free from interference by the closely-spaced adjacent compartment walls. Miniature size microphone and receiver transducers of this type suitable for tiny transistor-ampliiier hearing aids, present critical operating and space limitations, and they require careful and relatively diflicult More particularly, the invention relates to miniature size transducers of this type, the

Among the objects of the invention are alsol miniature Y acoustic signal transducers of the foregoing type, which within a given transducer size Will provide superior response characteristics.

The foregoing and other objects ofthe invention will be best understood from the following description of exempliiications theroef, reference being had to the accompanying drawings, showing all parts greatly enlarged, wherein:

Fig. l is a cross-sectional View of an acoustic-diaphragm transducer of the invention, Yshown with some of the adjacent elements of a complete transistor-amplifier hearing aid;

Fig. l-A is an elevational view of a transistor-amplier hearing aid as it is worn by the user, with the casing of the hearing aid enclosing'two acoustic diaphragm transducers shown in Fig. l;

Fig. 2 is a transverse cross-sectional view of the transducer of Fig. 1; i

Fig. 3 is a top view of the transducer of Fig; l, with the diaphragm and overlying casing wall removed;

Aso

.ducer windings of the transducer; Y

Fig. 6 is a top `view of the armature reed of the transducer;

Fig. S-A is an elevational view of the spool member of the ytransducer winding;

Fig. S-B is a cross-sectional view along line S-B-S-B of Fig. S-A;

Fig; 7 is a top view of the magnetic core assembly of the transducer; p

Fig. 8 is.,v a cross-sectional view along line 8--8 of Fig. 7; and Y Fig; 9 is a top view of a spacing shim for the transn ducer reed. l Y Y l In Fig. l is shown an end view of a complete transistor hearing aid the over-all dimensions of which are small enough to form a rearl portion 10 of a temple 11 of an eyeglass frame i2 worn by the user, as seen in Figa 1-A. `The over-all dimensions ofthe casing 10 of the hearing aid unit are such that itsvolume may be given a shape so that it lits in its entirety-together with the transistor circuits, battery and volume control-within thev concha cavity of the users ear between the tragus i `corresponding sound which is delivered to the ear canal of the user. Both the microphone transducer and the receiver transducer have essentially the same transducer structures, and they will now be described in connection with the acoustic microphone transducer 20 which is shown suspended within the hearing-aid casing 10 in Fig. 1, and also in Figs. 2 4.

The acoustic transducer 2.@ comprises a vibratory dia phragm Z1 which is connected through a drive rod 22 to a vibratory armature or reed 2S of an electromagnetic signal transducer structure having a 'spool 31 with transducer windings 39 wound thereon, Vand a cooperating ferromagnetic core structure generally designated 40. The armature reed 25 is of low-retentivity, high-permeability ferromagnetic material, and is shown as being of at cross-section and extending with its flat surface in a plane perpendicular to the surface of Fig. l. l n

The cooperating ferromagnetic core structure 4) cornprises one pair of pole arms 41, 51 extending transversely across and spaced from the opposite flat surfaces of the at a slight spacing on opposite sides thereof so that tlat reed end 26 is spaced from the two overlying oppositepolarity pole portions 42, 52 of the ferromagnetic core end areas yof the other dat reed end 29, and positioned p 2,927,977` l Patented Mar. `8, 196i) K at a slight air gap spacing on opposite sides thereof so that fiat reed end 29 is free to vibrate in the air-gap space between the two overlying opposite-polarity poles 44, 54 of the ferromagnetic core structure 40. The two pairs of pole arms 41, 5l and 43, 53 are shown formed of at sheet stock of low-retentivity, high-permeability ferromagnetic material, and their respective central poles 42, 52 and 44, 54 are given the desired opposite polarity by permanently magnetized core elements of the magnetic core structure 40. Although each of the two pairs of transverse pole arms 41, 51 and 43, 53 may form a distinct unit, the pole arms 41, :43 form two opposite integral arms of a generally rectangular ferromagnetic pole frame member 45 (Figs. 7 and 8), and the other two pole Varms51 and 53, `which Vare of opposite polarity, form two opposite integral arms of a similarly shaped ferromagnetic pole frame member 55. The two Vpole frame members 45, 55 form upwardly and downwardly facing opposite frame parts of the magnetic core structure 40, as seen in Figs. l and 2.

The desired permanent magnetic polarization and unidirectional eld is maintained at the pole pair 42, 52 and the pole pair 44, 54 of the magnetic core, by two elongated permanent magnet members or bars 49 (Figs. 2 and 8) having opposite outer faces held clamped between the overlying inward clamping faces of the two side arms of the oppositepole frame members 45, 55 extending generally parallel to the reed 25, as seen in Figs. l, 2 and 7, 8, and also in diagrammatic Fig 4. Each of the two permanent magnet bars 49 are magnetically polarized in a direction perpendicular to the at surfaces of the overlying pole frame members 45, 55, as indicated by the N and S signs applied to the core bars 49 in Fig. l, and in the diagrammatic view of Fig. 4.

The armature reed 25 may be pivotally supported in any known manner at its central region so that when vibrated as a microphone part in opposite directions on itsrcentral pivot support, the two opposite reed ends 26, 29 will approach one set of opposite-polarity core poles 42, 54 in one half-cycle of each vibration cycle, and will approach the other set of opposite-polarity core poles 44, 52 in the opposite half-cycle of each vibration cycle. As the two opposite reed ends 26, 29 so approach in opposite vibration half-cycles, opposite-polarity core poles 42, 54 and 44, 52, respectively, the permanently magnetized core 40 will induce in reed 25 oppositely-directed magnetic iluXes, respectively, indicated by single-head arrow 25-1 and double-head arrow 25--2 (Figs. 1, 4) and thereby generate corresponding oscillating electric signal currents in the surrounding transducer windings 39. When operating as a receiver, opposite half-'cycles of oscillating current traversing the transducer windings 39 will induce in the reed 25 oppositely directed magnetic polarizing fluxes indicated by the two opposite arrows 25-1, 25-2. As a result, the two alternately polarized reed ends 26, 29 will vibrate between the respective two sets of opposite-polarity core poles 42, 52 and 44, 54, in accordance with their alternating polarization.

In the acoustic transducer shown, one reed end namely reed end 26, is held clamped and fixed by central clamping screw 64 at a magnetic center position between the overlying opposite-polarity poles 42, 52 of the permanently magnetized core, so as to pivotally support the reed 25 for vibration with free reed end 29' in the air gap between opposite-polarity core poles 44, 54 (Figs. l and 2). When operating as a microphone, the acoustic diaphragm drive rod 22 vibrates the reed 25 in spool compartment 32, and the free reed end 29 will alternately approach the opposite-polarity core poles 44, 54 and similarly induce oppositely directed magnetic iluxes indicated by opposite arrows 25-1 and 25-2 in successive halfcycles of each complete vibration cycle and thereby generate corresponding oscillating electric signal currents in the surrounding transducer windings. When operating as a receiver, with the clamped reed end 26 heid ixed in the magnetic center between the overlying oppositepolarity core poles 42, 52, oscillating currents traversing the transducer windings 39 will induce in the armature reed 25, oppositely directed magnetic polarizing fluxes indicated by the opposite arrows 25-1, 25-2, thereby causing the free reed end 29 to vibrate in the air gap between its associated opposite-polarity core poles 44, 54 in accordance with the sequence of opposite polarizations imparted to the free reed end 29 during each opposite half-cycle of each complete reed vibration cycle.

in the transducer of Fig. 1, the opposite surfaces of the clamped, fixed reed end '26 are held spaced from the two opposite-polarity central pole portions 42, 52 or" the core structure 4i) by spacers or shims 61, 62, 63 so as to maintain the clamped pivot reed end 26 in the magnetic spacing center between the overlying opposite-polarity core poles 42, 52. When the transducer windings 39 of such transducer are not traversed by any. direct current of the transistor-amplifier circuit,'th'e magnetic spacing center coincides with the physical spacing center, and the clamped reed end 26 is held in the physical spacing center between the opposite-polarity core poles 42, 52 by nonmagnetic spacer shims of non-magnetic metal, for instance, of the same thickness. When the transducer windings 39 of such transducer ainplier hearing aid are traversed not only by alternating signal currents, but also by a direct-current component of the amplier circuits, such direct-current component imparts permanent directcurrent polarization to clamped reed end 26, thereby shifting the magnetic spacing center to a point other than the physical spacing center between the overlying opposite-polarity core poles 42,A 52. in order to maintain the clamped reed end 26 clamped in the true magnetic spacing center position between its overlying opposite-polarity core poles 42, 52, the clamped reed end 26 is shown held spaced from core pole 52 by a non-magnetic spacer shim 62 and a magnetic spacer shim 63, and the opposite side of the clamped reed end 26 is held spaced from the opposite-polarity core pole 42 by a non-magnetic spacer shim 61 of non-magnetic material the thickness of which is chosen to assure that the clamped reed end 26, which is additionally polarized by direct current through the transducer coil 39, is held clamped and retained in a true magnetic spacing center between the opposite-polarity core polesV 42, 52.

As indicated in Fig. 1, clamping screw 64 has a head overlying the outer surface of the depressed central core pole portion 42 of core arm 41, and it has a threaded rod'or shank which passes through corresponding aligned openings of core pole 42, reed end 26 and spacing shims 6l, 62, 63, and the threaded opening in similarly depressed, central core pole portion 52 provides for proper, positive mounting and clamping engagement of the clamped reed end 26 at the proper magnetic center posin tion between the core poles 42, 52. The other screws 65 passing through holes in opposite end portions of the other pairs of pole arms 43 and 53 of the two core frame members 45, 46, respectively, complete the clamping connections between the two pole frames 45, 55 across the two elongated permanent magnet bars 49 and join them into a relatively rigid unitary, self-supporting niagnetic core structure 40.

The elongated spool member or spool 31 of the transducer windings 39 (Figs. i-3 and detail Figs. 5 to 5-B) has a fiat cross-section corresponding to the cross-section of the reed 25 which it surrounds. The spool 31 has two dat spool Walls 32 enclosing between them a dat central spool compartment 33 within which the major part of the reed 25 is positioned for vibratory motion in the spool compartment 33 in a direction transverse or perpendicular to the majorA surface of the reed and the spool walls 32. The spool 31 has two end walls 34 of a height corresponding to the height of the surrounding core structure 4h, and side edges 35 which have fitting engagement with. inward side edges 46of thetwo pole frame members 55. Referring tty-Figs. l-3and detail Figs. 7, 8,'-the i two rgenerally rectangular core frameimembersAS, v55

` surround the frame space within whichfthe spool 3l .with its transducer windings are positioned. The distance between the opposite inward sidearm edges 46 of each pole frame member 45, 55 corresponds to the distance between the side edges 35 of the spool end walls 34, so as to receive with an aligning fit the lateral edges 35 of theAv spool end walls 34 and positively tix the transverse operatingV central position of the spool 3l between the side arms of the pole frame members 45, 55. The distance between the facing frame corner edges 47 which extend perpendicularly to the side frame edges 46, corresponds to the longitudinal distance between the outer surfaces 36 of the spool end walls 34 so' yas .to receive with an aligning' tit and positively-locate the end surfaces 36 of the spool end walls 34 and positively locate the longitudina operative position 'of the spool 3l. p

in mini-ature acoustic signal transducers of the present invention, where space limits are critical, the distance between the spool compartment walls 32 (Fig. -S-B) which dene the operative compartment heightacross which the armature reed 25 vibrates, must be kept to al Thus, in a miniature transducer. operating minimum. with a magnetic armature-'reed having aV thickness of .010", it is desirable to keep the height Y'of the spool to avminimum. at which their inwardly facing surfaces will remain free from the slightest interference with the freeiy vibrating portions of reed 25 held betweenv them. As example, in the specilic transducer shown, it is desirableto keep the distance lbetween the facing spool walls 32 at about .026if33l. The minute dimension tolerance of .001" inthe height dimension of such spool is needed for enabling production of such spools on a practical basis, as by molding with a resin, without pro-.A hibitive shrinkage losses.

In assembling the components of such 'miniature transducer, critical problems areencountered in the proper positioning of the spool 31 in relation to the core 40, for

assuring that the spool compartment walls 32 areat the f proper critical distance from the opposite surfaces ofthe yibratory reed 25. Even with skilled operators, excessive production shrinkage is caused vby failuresv in theV required accurate positioning of the spool 3l with respect to the magnetic core 40, that wouldeliminate interference with the free reed vibrations'in the assembled transducer, and avoid prohibitive shrinkage losses.

In accordance with the present invention, the critical difficultiesencountered in the accurate positioning ofthe spool compartment walls 32 relatively ,to the major surfaces of the vibratory reed 25 when assembling such miniature transducers, are substantially overcome by providing the spool end walls 34 at a plurality of peripherally spaced regions thereof with outwardly extending aligning projections or members of a height corresponding exactly to the operative spacing of the two opposite pole frame members45, 55, and arranged for aligning engagement with peripherally displaced portions of the assembled core frame members 45, 55. Since the spacing of the two pole frame members 4,5, 55 deiines the spacing .of their two sets of opposite-polarity pole pairs 42,: 52 and 44, 54 and the magnetically centered operative position of the reed 25, such peripherally displaced aligning projections of the spool 31 makes it possible to assure that in the assembly of the transducer components, the two spool compartment walls 32 are automatically positioned in the required critical spacing -relation relatively to the vibratoryv reed 25 extending therethrough.

Referring to Figs. 1-3, and detail Figs. 5-5-B, each spool end wall 34Vis provided along its outward end wall Ksurface 36pl with two spaced outwardly projecting spool aligning -shouldersgorprojections 37 extending Vparallel to the direction of the v ibratory motion of the` reed .25. ,Each of the four spool aligning projectionsl 37 has a pair of accurately positioned transversespool aligning r.surfaces 38 which define the height at whichthe assembled core pole frames 45, 55 are'engaged by them sopas to assurethat they are placed in theaccurateioperative .position `wherein the central spool compartment fwalls 32 remain free from interfering engagement withthe ",vibratory reed 25 passing therethrough. The spacing'ofi each pair of spool aligning surfaces 33 is identicalwith thefspacing ofthe facing upper and lower 'surfaces'of the permanent magnet core bars 49 (as seen in Figs. l andl 3) ywhich are held clamped between the twocore vrame-members 45, 55. -The four aligningprojections 37 of thespool 31 are located at four peripherally displaced outward portions of the spool structure 31, thereby assuring that the four aligning shoulders 37 will engage four peripherally displaced cooperating. aligning surfaces at the four corners ofeach of the two outer core pole frames 45, 55, and enable'accurate aligned position- `ing and assembly of the core elements 45, 55, 49,-the spool 31 and the reed25 into the composite, operative transducer unit 40 shown. By providing the tiny spool 31 with the four peripherally displaced aligning shoulders 37 along the outward surfaces of the spool end walls 34, the assembly and accurate positioning of the spool with I 'compartment 33 or the distance between'its flat walls 32 the other elements of the composite transducer structure is thus greatly simplified. By way of example, such assembly vmay be performed as follows:

In a suitable jig, there is first positioned the lower core pole frame 55. After placing on the transverse core pole52 the proper lower spacing shim or shims, such as spacing shims 62, 63, the reed 25 with the spool v31 and the transducer winding 39 previously positioned over the reed, are dropped into the jig which alignsv them in their Vproper positions with the spool end walls 34 -tting between the two inward side edges 46 and the four corner edges 47 of the lower core frame member 55. This brings the four downward spool aligning surfaces 38 of the spool 31 (as seen in Figs. l, 2, 5 in aligning contact engagement with four peripherally spaced align- 4ing corners 47 of the lower pole frame 55. Thereupon the upper pcie frame member is placed in the jigY wherein Ait is yautomatically aligned over the component assembly, in which position the inwardly facing surfaces of the four inner corners 47 of the upper frame 45 automatically come into aligning engagement with the peripherally displaced upwardly. facing spool aligning surfaces 38 of the f our spool aligning projections 37, thereby automatically assuring that the spool 31V with its closely spaced compartment walls 32 will be properly aligned with respect to the two core pole frame members 45, and therethrough with respect to the vibratory transducer reed 25. The assembly is completed by `screwing in position the three clamping screws 64, which join the assembly into the operative transducer unit.

The outwardly extending aligning spool projections 37 do not increase the over-all dimensions of thetransducer assembly because the spool-aligning projections 37 merely occupy space available at the four inner corner regions of the generally rectangular core assembly 40 of the transducer. The aligning spool projections 37 also make it possible to provide the spool body 31 around which the transducer windings are wound, with the required rigidity while reducing to a minimum the lateral space occupied by the walls of the spool compartment 33, as seen in Figs. 1-5 and S-B. The reduction of the lateral space occupied by the walls of the spool compartment 33 of the winding spool. 31 is secured by eliminating the 2" l side walls ofthe spool compartment and utilizing as winding support only the two flat Vspool compartment walls 32 bordering the upper and lower sides of the minute spool compartment 33, as seen in Figs. 1 5 and 5-B. The required additional rigidity that would be supplied by compartment side walls, is provided by the four aligning projections 37 which serve as four reinforcing members extending transversely to the two spool compartment side walls 32 and give them the rigidity required for providing the proper support for the transducer windings, 39 and assure that the two `spooi compartment walls 32 are not deformed under strain and are maintained at the correct spacing of the spool compartment 33 free of interfering engagement with vibrating portions of the armature reed 25.

In mainiature transducers of the foregoing type, it is desirable to utilize highly permeable ferromagnetic material, for instance the material known Yas Hymn 80, for the resilient, vibratory reed 25. The limitations on the minimum required cross-section and on the length of the vibratory reed 25, make it diicult to obtain a reed of such highly permeable magnetic material which will operate with the compliance required for optimum transducer sensitivity. In accordance with the invention, the vibratory ferromagnetic reed is given the desired greater compliance within the required minimum length and thickness dimensions, by arranging the clamping connection of the clamped reed end 26 in such manner as to permit free vibration of a part of the clamped reed end 26 vwhich would normally be held clamped and restrained against vibration. The novel arrangement of the clamped reed end 26 which increases the free vibrating length of the reed, while assuring that the clamped reed end is properly maintained in its clamped operative position, will now be described (Figs. l, 2, 6 and 9).

In the accepted prior-art practice, the spacing shims 61, 62, 63 with which the reed was held clamped between the facing pole portions 42, 52 of the two pole frames 45, 55, normally extended over the entire area of the reed end 26, which is embraced by the two pole portions 42, 52, of core frames 45, 55. In accordance with the invention of Harry A. Pearson, assigned to the assignee of the present application, the dimensions of the spacing shims, and particularly of the Vnon-magnetic shims 61, 62overlying the clamped reed end 26, are limited along the lons gitudinal direction of the reed 25 only up to at most threequarters of the reed area embraced by the core poles 42, 52. ln the arrangement shown, the two spacer shims 61, 62 have the shape shown in Fig. 9. Each shim, such as shim 61, has two arms extending from its outer edge along both sides of the fastening member or clamping screw or rod 64 to the inward edge of the screw opening 61-2 through which the clamping screw 64 passes. The soforrned shims 61, 62 of theV clamped reed end 26 conne the clamping engagement to the outward edge region of the clamped reed end and two rear portions of the adjoining reed mounting portion embracing the clamping screw 64 which are in clamping engagement with the inner edge 61-2 of the adjacent overlyng spacing shims 61, 62. In addition, the part of the clamped reed end 26 with the reed opening 26--1 (Fig. 6) through which the screw 64 extends, is enlarged in the adjoining inward reed region extending beyond the overlying inner spacer shim edges 61-2, thereby providing the free inward reed portions adjoining the clamped reed end 26 with two ilexible resilient reed junction arms 25-4 having a raidal dimension shorter than the radial dimension of the adjoining reed portions which are held clamped between the shims 61, 62. This makes it possible to give the reed 25 the desired greater compliance and secure operation thereof with the desired resonant mode at which the acoustic transducer will operate with desired overall response.

Circuit connections from the coil winding 39 to cooperating exterior surfaces may be provided Iin any conternalends of the two insulated conductor leads 56 are stripped of their insulation and are electrically affixed, as by solder, to two spaced metallic transducer terminals 57, to which the transducer windings -39 are connected. The transducer terminals 57 are mounted on an underlying terminal support which is mounted on the transducer unit 40. The insulating support for the transducer terminals 57 may be formed of overlapping layers of insulating sheet material, for instance resin-impregnated cloth, holding between them one leg of two tiny U-shaped terminals 57, leaving one terminal leg 57 exposed for connection to the stripped conductor lead ends 56.

Miniature acoustic transducers of the type described herein, usually also have a casing or cup 71 of suitable metal, for instance, brass or aluminum, within which the transducer assembly is mounted. The transducer structure is suitably affixed to the casing 71, for instance, as by placing four drops 73 of cement along spaced peripheral regions of the upwardly facing core frame member 45 where it adjoins the casing side walls 72 (Fig. 3).

The casing 71 has side walls or a rim 72 with a rim edge to which the edge of diaphragm 21 is secured, as by cement. The casing 71 may be of magnetic shield material, where it is desired to magnetically shield the electromagnetic elements of the transducer against magnetic interlinkage with disturbing magnetic elds of another similar transducer, for instance, for suppressing magnetic feedback interlinkage between the electromagnetic elements of a microphone transducer and receiver transducer forming parts of a transistor hearing aid. The casing 71 may be made of a non-magnetic metal, and where a shield enclosure is desired, `an outer magnetic shield casing or cup 74 is placed in contact with and over the interior housing cup 71. A cover wall 75 of metal, overlying the exterior side of the vibratory diaphragm 21, has a rim which is joined, as by cement, to the casing 72. Acoustic excitation of the diaphragm 21 or delivery of generated sound, may be obtained by providing the casing cover 75 with one or more acoustic openings.

After the internal transducer unit 40 is assembled in the casing 71 and before the diaphragm 21 is aixed thereto and to the casing, the operative position of the vibratory reed 25is checked to assure that it is in the magnetic center beween he adjacent poles 42, 52 o'f the core structure. Although proper choice of the magnetic shim in relation to the magnitude of the direct-current traversing the coil windings 39 will secure proper 'mag netic centering of the mounting end 26 of the armature reed, additional minute adjustment of the reed position is desirable to' assure optimum operation of the transducer. Such minute adjustment of the reed 25 may be effected by applying to the upper or the lower side of the reed 25, as seen in Fig. l, the tip of a bending pin or rod for giving it a minute permanent bend in one or the other direction to bring the reed 25 to its optimum operating position. The optimum operating position may be checked by connecting the transducer windings to an iustrument, for instance an oscilloscope, and observing the response of the transducer unit 4@ over a critical frequency range thereof. In the transducer sho'wn, such setting tool may be applied to the portion of the reed 25 which is exposed in the transducer unit 4t) between the inward edge of the core-pole pair 42, 52 and the adjacent spool end walls 34, as seen to the left in Figs. 1 and 3, the tool being applied in the direction of o'ne of the arrows 66. in order to make it possible for such setting tool to be applied to the reed in the direction of arrows 66 while assembled in casing 71, this casing 'and also the shielding casing 74,'if used, are provided with an'o'pening7l-2, thereby exposing at the: opening 71,-2`the downward facing side ofreed 25 to the tool for giving it einem?? transducer `and thereby enhances the response ofgthe the nal adjustment setting. After the setting of the reed A.

is completed, thecpeningifi-Z rmay be closed as by terial, having opposite end tongue portions secured to the outer surface portions of thel transducer casing 71 and the hearing-aid casing 10, respectively, inwhichit is carried. i,

TheV acoustic responses of a transducer of the typedescribed-above, are controlled by the -acoustic characteristics of the interior transducer compartment 69 bounded by the inner Vside of diaphragm 21 and casing 71, and of the outer diaphragm compartment 76 bounded bythe outer side of diaphragm 21 and the outer casing cover 75. in Vthe transducer shown, the acoustic connection from the outer diaphragm compartment 76 to the exterior space (inthe case of a microphone) or to the ear canal (in the case of a receiver), is provided by a sound chan-- nel or passage 77 extending along the casing rim Wall 72 of the casing 7l. In accordance with the invention, the side rim wall 72 of casing 71-is formed with an in-l wardly recessed channel-shaped wall portion 81 extending from the level ofthe diaphragm 2i to an inward wall level, ,and a cover wall 82 is affixed, as by cement or solder, to the recessed channel-shaped wall portion 81 of casing rim 72 to form the desired sound channel 77 between the outer diaphragm compartment 76 and the exterior space. A cover wall opening 83 connects the sound channel 77 to the exterior space. Thevibratory diaphragm 21overlyng the upper end of thev sound channel 77 (as seen in Fig. l) has an opening 21-'1 through which the channel passagev77 is connected to the diaphragm front compartment 76, thereby completing an acoustic connection from the exterior space to the outer diaphragm compartmentspace 76.Y In the vcase of a hearing aid,rthe channel opening 83 of the, sound channel 77 is suitably connected either lto the exterior space when operating as a microphone for exciting the diaphragm by exterior sound, or to the ear canal of the user for delivering or propagating the sound generated in the front` diaphragm compartment 76 to the ear canal of the user. In Fig. 1, the transducer is shown operating as a microphone which is excited by sound propagated from the exterior space through sound channel 77. i

The sound channel openingV 83 of the sound passage 77 is connected to a casing-opening 10- 1 of the hearingaid casing through acoupling channe1 8S (Fig. 1) for the transmission of sound propagatedin the Vsurrounding space through casing opening 10-1, sound passage 86 receiver over the lower frequency range., i' Thus, in the lspecific form of transducer shown, the acoustic passage l connection 77 from the outer diaphragm compartment 76 to the exterior space is dimensioned to provide an acoustic mass impedance which lowers the resonant frequency of the transducer system from about 2000 c.p.s. Y (cycles per'second) 'to 1400 c.p.s., or in general, to a resonant frequency in the range between 1300;c.p.s. and 1500 c.p.s. Such acoustic passage connection-*to the exterior space may be readily designed, as by restricting Y its cross-section over a specified length thereof, for raising its acoustic resistance and thereby damp the peaked transducer response at its resonant frequency.

outer diaphragm, compartment to the exterior space with Y a recessed casing wall channel of the transducer casing rim, the sound .connection to the surrounding space is i provided 'along a side wall or rim of the transducer casing. Such acoustic connection along the vrelatively short'side wall of the transducer casing eliminates'the problems encountered in miniature all-in-one hearing aids when lrnaliinganacoustic. Vconnection to the diaphragm compartment openings of an acoustic transducer through an opening in acasing such as casing wall 75 overlying the diaphragm 21. l

4In. accordancel with a phase of the invention, such inwardly recessed channel-shaped wall portionof the transducercasing, such as transducer casing 71, is utilized in conjunctiony with an outer coverportion such as cover wall 32 to provide a sound passage of predetermined jacoustic characteristics through which one of the transducer compartments is" connected either to theA exterior space or tanother transducer compartment and thereby modify or control the acoustic response of the transducer f over a predetermined frequency range. In addition, such `acoustic channel passage or restricted cross-section may A be used, for instance, in the manner described in Knauert engaging the surface of the-casing 10 surroundng'casing Y :Patent 2,820,107-, for raising the frequency response of a microphone between 200 andl600 c.p.s. A In the transducer, shown, the inner transducer compartment 69' has interior transducer compartment an acoustic system.

There will now be described one manner in which an acoustic passage channel formed by an inwardly-recessed, channel-shaped wall portion of transducer casing '71, is utilized for similarly raising the frequency response of a microphone in the lowfrequency range, for instance between 400 andv 600 c.p.s., orin general, between y200 and 600 c.p.s.

In the transducer shown, the recessed portion of rim side wall 72 of the transducer which forms with casing cover wall 82 the recessed sound channel 77, has further recessed channel wall portions 91 and 92 which form `with casing cover wall 82 an additional sound passage 93 which contacts sound channe1 77 Vto the interior transducer compartment 69. The recessed wall portion 92 Vof the additional acoustic channel or passage 93 has an acoustic opening 94 below the level of the diaphragm 21, through which the space of additional sound passage 96 is acous- .tically connected to the inner transducer compartment 69. The acoustic impedance of the additional channel passage.

channels for forming acoustic passages connected to an acoustic compartment of the transducer for modifying or By forming the acoustic passage connection from thel In a similar way, other wall portionsY of the transducer casing 71 may be provided with recessed l controlling Vthe responsev of the transducer in a selected part of its frequency range.

The cover wall 82 which forms with the recessed channel-shaped portions of casing rim wall 72, the sound channels 77 and 93, described above, may be of a dimension just sufcient to slightly overlap the width of the passage, the cover wall portion 82 being secured to the underlying wall portion of the casing rim Wall 72, as by cement or solder. In the arrangement shown, a single cover wall member 82 is secured to the recessed channelshaped wall portions 81, 92, of the casing side wall, for forming therewith the two sound passages 77 and 93. Where the microphone casing 71is provided with a magnetic shield, cover wall 82 may be formed of ferromagnetic high-permeability material and may form part of the magnetic shiled 74 seated over the inner casing wall 81 and forming a magnetic shield enclosure around it.

By way of example, there are given below, construction data of a practical embodiment of the inventionv in the form of a miniature microphone transducer of a hearing aid:

Reed.-HYMU 80 magnetic material; .010 thick; .300"

long; .100" wide, with mounting end .135" wide. Di-

ameter of reed opening .021" to .047"; width of two reed arms beyond reed opening .037 to .050" depending on desired response. g Cut-off spacer shim for reed-Brass; thickness either 0.002; 0003"; 0.0035"; 0.004, depending on desired response. Distance from opening center to rear edge, .040", and to shorter front edge .010". Permanent magnet cores.-Alnico v2; .330 long; .070" in height; .067" width.

Pole arm frames.-Alloy of 50% N, 50% Fe; .025" thickness; .080" pole arm width; .055" side arm width; .215 spacing of inner side arm edges; .218" spacing of inner pole arm edges.

Spool-Nylon; .150" total length; .009" thickness; .115

height; .188" width of reed compartment; .009 thickness of compartment side walls; .026" height and .118" width of reed compartment; .009 thickness of Vtornpartment side walls. Y

Spool-aligning projections- .070" height transverse to reed; .016" projection length and end area Width.

Main casing-.008 wall thickness; .170 inside height; .436" by .336" inside area; .021 channel-recess depth, and .042 channel recess width.

Aluminum foil diaphragm-.0005 foil thickness of receiver; .0007" thickness of microphone.

The claims in the present application are directed to a miniature-size acoustic transducer device wherein the sound outlet from the diaphragm compartment is formed by a channel recess along the short side wall of the transducer casing instead of along the wide casing wall overlying the diaphragm. Other features of the invention disclosed herein constitute the subject-matter of the co-pending applications, Serial No. 774,438, filed on November 17, 1958, by W. F. Knauert, and Serial No. 774,439, filed November 17, 1958, by Harry A. Pearson, and assigned to the assignee of the present application.

It will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection With specific exemplications thereof will suggest various other modifications and applications of the same. lt is accordingly desired that in construing the breadth of the appended claims, they shall not be limited to the specific exempliiications of the invention described above.

I claim:

1. In an electromagnetic acoustic transducer device for transducing electric signals into acoustic signals or vice versa, a ferromagnetic armature arranged to vibrate transversely to a major dimension thereof, a cooperating ferromagnetic core structure extending adjacent said armature and forming therewith at least one ferromagnetic core loop carrying a magnetic ilux which uctuates in accordance with the armature vibrations, transducer windings interlinked with the core loop and responsive to the flux fluctuations thereof for transducing vibratory motion of the armature into corresponding electric-signals passing through the windings and vice versa, a vibratory diaphragm having an intermediate portion connected to said armature for transmitting vibrations therebetween, an inner casing section having a rim wall surrounding an inner casing compartment, the peripheral region ,of said diaphragm being joined to said rim wall for enclosing said armature said core structure and said windings in said inner compartment, an outer casing section overlying the outer side of said diaphragm and forming with it a front compartment, said rim wall having an inwardly recessed channel-shaped wall portion extending from the level of said diaphragrn'to an inward level of said rim wall spaced from said diaphragm, a cover wall overlying and afl'lxed to said channel-shaped wall portion and forming therewith a sound channel extending from said diaphragm to said inward level, said cover wall having in the region of said inward level, a cover opening acoustically connecting said channel to the exterior space, said diaphragm having a diaphragm opening through which said front compartment is acoustically connected to said sound channel and therethrough to the exterior space for propagation of sound between said front compartment and the exterior space.

2. In a transducer device as claimed in claim 1, said rim wall having a further recessed channel-shaped rim wall portion extending from the region of said cover opening to a further rim wall portion peripherally clisplaced from the cover-opening region, a further coverwall portion overlying and aixed to said further channelshaped rim wall portion and forming therewith a further sound channel extending from the region of said cover opening to said further rim wall portion, said further rim wall portion having a rim opening acoustically joining said further sound channel and said interior compartment into an acoustic system which resonates within a selected frequency range between 200 and 600 cycles per second forV raising theresponse of said transducer device over a region of said selected frequency range.

3. In a transducer device as claimed in claim 2, said cover walls being formed of ferromagnetic high-permeability material and being part of a shield enclosure enclosing at least said inner casing section for suppressing magnetic interlinkage between -the ferromagnetic core elements and windings of the transducer device with external magnetic flux.

4. A transducer device as claimed in claim l, said cover walls being formed of ferromagnetic high-permeability material and being part of a shield enclosure enclosing at least said inner casing section for suppressing magnetic interlinkage between the ferromagnetic core elements and windings of the transducer device with external magnetic flux.

5. In an electromagnetic acoustic transducer device, an elongated dat ferromagnetic reed armature arranged to vibrate transversely to its length between two opposite end positions and having two armature ends, a hollow spool member having an elongated interior space in which the major length of said armature is held for vibration therein in a direction transverse to its length, transducing windings surrounding and held by said spool member, a ferromagnetic core structure comprising two elongated core bodies extending parallel along opposite sides and confining between them said spool member and one pair of ferromagnetic pole-arms extending transversely to and on opposite sides of each of the two dat armature ends between said two elongated core members and forming therewith two substantially closed ferromagnetic core return paths of opposite polarity in the opposite end positions of said armature and thereby causing vibratory motion of said armature to generate corresponding .electric oscillations in said windings and vice versa, a vibratory diaphragm having an 'intermediate'.v portion connected to saidarmature for transmittingsyi-v brationsjtherebetween, an inner casing section having a rim wall lsurrounding an inner casing compartment, the peripheral region of said diaphragm being joined to said rim wall for enclosing said armature said core structurel extending from the level of said diaphragm to an inward t level spaced from said diaphragm, a cover wall overlying and affixed to said channel-shaped wall portion and formf ing therewith a sound chanel extending from said dia-V phragm to said inward level, said cover wall having in the region of said inward level a cover opening acoustically connecting said channel to -the'exterior space, said diaphragm having a diaphragm opening through'which said front compartment is acoustically'connected to said sound channel and therethrough to the exterior space for propagation of sound between said front cornpartn ment andthe exterior space.

.6. In a transducer device as claimed in claim 5, said rim wall having a further recessed channel-shaped rim wall portion extending from the region of said cover opening to a further rim wall portion -peripherally displaced from the cover-opening region, a further cover wall portion overlyingV and axed to said further channelshaped rim wall portion and forming therewith a further sound channel extending from the region of said cover opening to said further rim wall portion, said further rim wall portion having a rim opening acoustically joining said further sound channel and said interior compartment into an acoustic system which resonates within a selected frequency range between 200 and 600 cycles per second for raising the response of said transducer device over a region of said selected frequency range.

7. In a transducer device as claimed in claim 6, said cover walls being formed of ferromagnetic high-permeability material and being part of a shield enclosure enclosing at least said inner casing section for suppressing magnetic interlinkage between the ferromagnetic core elements and windings of the transducer device with external magnetic ilux. Y

8. In a transducer device as claimed inclaim 5, said f cover walls being formed of ferromagnetic highpermea bility material and being part of a shield enclosure enclosing at least saidv inner casing section for suppressing magnetic interlinkage betweenV the ferromagnetic core elements and windings of the transducer device with ex.- ternal magnetic flux.

9,' In an electromagnetic acoustic transducer device for transducing electric signals into acoustic signals or vice versa, a ferromagnetic armature arranged to vibrate f transversely to a'major dimension thereof, a cooperating ferromagnetic core structure extending adjacent said armature and forming therewith at least one Yferromagnetic core loop carrying a magnetic flux which uctuates in accordance with the armature vibrations, transducer windings interlinked with the core loop and responsiveto the flux uctuations thereof for transducing vibratory motion of the armature into corresponding electric signals passing through the windings and vice versa, a vibratory dia phragm having an intermediate portion connected to said armature for transmitting vibrations therebetween, an

inner casing section Vhaving a rim wall surrounding an inner casing compartment,y the peripheral region of said diaphragm being joined to said rim wall for enclosing said armature, Ysaid core structureand said windings in said inner compartment, an outer casing section overlying the outer side of said diaphragm and forming with it a front compartment, a casing wall of said inner casing section having an inwardly recessed channel-shaped wall portion of restricted transverse dimensions, a cover wall overlying and aixed to said channel-shaped wall portion and forming vtherewith a sound channel, the length of said sound channel being at least about five times the average transverse dimension of said channel, a certain small wall portion of a wall bounding said channel having one channel opening acoustically coupling the space of said channel to the space of one of said compartments.

10. In a transducer devicel as claimed in claim 9, a

n' further wall portion of a Wall bounding said channel No references cited. 

